This invention relates in general to apparatus for working on sheet material and deals more particularly with improvements in automated apparatus for plotting on or otherwise marking sheet material. An apparatus of the type with which the present invention is concerned includes a carriage assembly which moves a marking instrument or pen relative to a sheet of material or plotting paper spread upon a supporting surface in response to command signals received from a controller.
In a plotting apparatus of the aforedescribed general type it is generally desirable that the pen be arranged for rapid movement into and out of marking engagement with the plotting paper. At the begining and end of each plotted line it is usually necessary to momentarily halt the instrument carriage, which supports the gas, while the pen is moved into or out of marking engagement with the paper. Consequently, it is desirable to minimize the distance through which the pen moves between positions of marking engagement and disengagement with the plotting paper to enable rapid response. Heretofore, mechanically actuated linkages have generally been utilized for moving the marking instrument into and out of marking engagement with the plotting sheet. Since such mechanical systems are prone to vibrational movement, substantial clearance must be maintained between the plotting surface and the marking instrument when the instrument is out of marking engagement with the plotting sheet to prevent accidental marking due to vibrational movement of the plotting instrument and to compensate for irregularities in the plotting surface. Also, response time is increased by acceleration and deceleration of connecting linkages actuating the pen or marking instrument. Further, the carriage assembly which moves the instrument is subjected to frequent acceleration and deceleration during the normal plotting operation. The aforementioned conditions tend to increase apparatus response time and thereby reduce plotting speed. The present invention is primarily concerned with the aforementioned problems.